High Ki-67 labeling index in human colorectal cancer with microsatellite instability

In the present study, we examined the relationships between microsatellite status and Ki-67 labeling index, a proliferative marker, in colorectal cancers in order to clarify the common biological profiles of familial and sporadic cases of MSI (microsatellite inability)-positive tumors.Seventy-eight invasive colorectal carcinomas were studied. Five microsatellite loci were analyzed by polymerase chain reaction, while Ki-67 was studied by immunohistochemistry.The MSI was found in 15 (19.2%) of the 78 tumors, and the Ki-67 labeling index was significantly higher in the 15 MSI-positive tumors than that in the 15 MSI-negative ones (p = 0.0181). Moreover, the Ki-67 labeling index was significantly higher in the 7 tumors with MSI at more than 2 loci (MSI-H; high-frequency MSI) than that in the MSI-negative ones (p = 0.0082).The present study demonstrates that colorectal cancers with MSI show high Ki-67 labeling index irrespective of hereditary or nonfamilial cancer types, suggesting their common biological aspects distinct from MSI-negative ones.